This application pertains to the art of joints and, more particularly, to flexible joints for conduit. The invention is particularly applicable for use in jet engine bleed air duct systems and will be described with reference thereto. However, it will be appreciated that the invention has broader aspects and may be used in any conduit system wherein limited flexing of joints is desirable for relieving high thermal and structural stresses by deflecting under low bend loads.
It is conventional on jet aircraft to bleed air from the engine compressors for such purposes as aircraft air conditioning, heating, pressurization and de-icing. The ducting for such bleed air is subjected to a wide range of temperatures and high bend loads are imposed on duct joints as a result of thermal expansion, particularly, in the ducting takeoff from the bleed pad to common manifolds. In order to withstand the high bend loads, stronger manifolds and joints have been used. However, this simply stiffens the ducting at the joints and bend loads become even greater.
Flexible joints have been proposed for deflecting under the bend loads and such flexible joints have been made using metal bellows. Flexible metal bellows are subject to fatigue failure and are not highly reliable. In addition, a metal bellows requires a pneumatic joint on each of its opposite ends.
It would be desirable to have a reliable pneumatic joint which was capable of taking the necessary deflections in ducting of the type described, while being readily assembled and disassembled.